A variety of different refrigeratable dough products are currently available to consumers to produce different sorts of baked products. Products containing ordinary baker's yeast, however, may only be stored for quite a limited period of time since, even under conditions of low temperature, the yeast shows substantial activity resulting in a consistent production of carbon dioxide. This continuous development of gas eventually results in leavening of the dough during storage, i.e., in the refrigerator. Moreover, the continued activity of the yeast beyond the desired degree of proofing deleteriously affects the organoleptic and rheological properties of the dough, resulting in final baked products that are unacceptable.
For this reason most of the commercial dough compositions do not contain yeast to leaven the dough. Rather they contain chemical agents, so that they may be stored for a prolonged period of time without occurrence of the known detrimental effects of yeasts. The advantage of such chemical leavening agents is that their behavior is based on a predictable chemical reaction, thus, allowing control of the volume of carbon dioxide produced to leaven the dough. Although the storage lifetime of products leavened by means of chemical agents may be extended, the final baked goods obtained therewith are known to be inferior compared to products leavened by means of baker's yeast. In particular, the texture of the products is often not acceptable to customers. The products also lack flavorings produced by the yeast during its activity.
Another approach to avoid the problems encountered with the use of yeast in dough compositions under long term storage at refrigeration conditions, is to store the yeast containing dough, optionally in pre-baked form, at freezing temperatures of about −20° C. to reduce the activity of the yeast to a minimum. To this end U.S. Pat. No. 5,385,742 teaches the use of a dough composition that utilizes the substrate limiting concept. Accordingly, a dough is leavened with a maltase negative yeast and is subsequently frozen for long term storage.
This approach, however, has also been shown to be unsatisfactory in that products prepared from frozen dough compositions are not as convenient for the consumer as are refrigerated dough products. The frozen dough has to be thawed and, in most instances, pre-proofed prior to baking. Furthermore, the pre-proofing has to be monitored by the consumer to avoid extensive proofing of the dough. Moreover, the texture of the final baked product derived from frozen dough has been shown to be inferior to products produced from non-frozen dough. Furthermore, the characteristic flavor associated with yeast leavening is inferior or often completely lacking.
Recently low temperature inactive strains of baker's yeast (lti-strains) have been developed. These yeast strains are essentially inactive at low temperatures, but retain their activity when brought to higher temperatures.
U.S. Pat. No. 5,399,492 describes a process for constructing yeast strains having the lti-property, wherein a strain of saccharomyces cerevisiae is subjected to a mutagenic treatment, at least one mutant having an lti-property is selected and is backcrossed at least once with a wild type haploid strain of saccharomyces cerevisiae having an opposite mating type, at least two backcross segregants having an lti property and opposite mating types are then selected and are crossed at least once, and a diploid strain having a growth potential, a lti-property, and the ability to raise a dough is selected.
The construction of different lti-derivatives has also been described. In U.S. Pat. No. 5,776,526 there is described a process for constructing lti-strains that react more slowly with the maltose contained in the dough. These strains may be obtained by crossing a haploid saccharomyces cerevisiae having an lti-property with a haploid saccharomyces cerevisiae strain having an active maltase gene, that is under catabolic repression, subsequently crossing the segregants and selecting a diploid strain showing an lti-property, an active Mal-phenotype (Mal(+) expressing the gene coding for maltase either inducible (wild-type) or constitutively), and having growth potential.
For a dough composition to be stored at refrigerator conditions and to eventually result in a baked product having the desired texture and excellent flavoring the activity of the yeast in the dough must be carefully controlled. To this end the activity should not be entirely null during storage, since otherwise an unacceptable texture will be formed and no flavorings will be produced. An extensive activity of the yeast, however, is known to lead to excessive leavening of the dough during storage with the flavor deteriorating with continuing metabolic action of the yeast.
With regard to using current yeast-strains having an lti-property, these strains have been found to produce dough with good texture and flavor properties only in a time range of refrigerated storage between 2 and 3 weeks. The dough tends to be underdeveloped in the first week and overdeveloped or even deteriorated between 4 and 5 weeks.
To date scientists have not been able to develop dough compositions that provide the desired properties, over the entire shelf life of the dough, i.e., to provide a yeast containing dough composition having an activity that is necessary to provide baked products having the same or a similar texture and flavor as compared to products prepared from freshly prepared dough.